How do astronomers explain the size of the universe?

Following the discovery that the universe is expanding and that this expansion is accelerating, scientists developed a method to measure distances within galaxies using light/Doppler theory. The theory is quite straightforward: when an object emits light, it compresses toward the blue end of the spectrum; when it moves away, the light waves lengthen toward the red end of the spectrum, which is known as the "red shift." Next, they use the light of a specific type of star, known as a Cepheid, as a baseline of candle power, a measure of the strength of light observed. Because the Cepheid is extremely stable, using these stars as measuring points and measuring their candle power plus the amount of red shift allows scientists to estimate the distances between stars and galaxies.

Astronomers explain the size of the universe by observing the expansion of space-time and measuring the distances to celestial objects using various techniques such as parallax, standard candles, and redshift. They also utilize mathematical models, such as the Friedmann equations, to describe the large-scale structure of the universe.